NASA astronomers announced the discovery of a strange super-Neptune circling a pair of orange and red dwarfs known as Kepler-413.
This is an artist’s impression of an extrasolar gas giant. Image credit: NASA / JPL-Caltech.
The exoplanet, dubbed Kepler-413b, is a circumbinary gas giant of about 65 Earth masses located in the constellation Cygnus, about 2,300 light-years away from Earth.
It orbits its host star every 66 days at a distance of about 0.355 AU (astronomical units).
Kepler-413b is very unusual because it wobbles wildly on its spin axis, much like a child’s top. The tilt of the spin axis of the planet can vary by as much as 30 degrees over 11 years, leading to the rapid and erratic changes in seasons. Contrast this to the rotational precession of our planet – 23.5 degrees over 26,000 years.
Analyzing data from NASA’s Kepler Space Telescope, the team led by Dr Veselin Kostov form the Space Telescope Science Institute and the Johns Hopkins University in Baltimore found an unusual pattern of transits for Kepler-413b.
“What we see in the Kepler data over 1,500 days is three transits in the first 180 days, then we had 800 days with no transits at all,” Dr Kostov said.
Normally, transiting planets are seen passing in front of their parent stars like clockwork. Kepler finds such planets by noticing the dimming of the parent star as the planet travels in front of one of them.
“After that, we saw five more transits in a row,” said Dr Kostov, who is the lead author of a paper accepted for publication in the Astrophysical Journal (arXiv.org).
This image shows the unusual orbit of Kepler-413b around a pair of orange and red dwarfs. The vertical axis on the right panel is exaggerated by a factor of 10, for viewing purposes only. Image credit: NASA / ESA / A. Field, STScI.
The next transit is not predicted to occur until 2020. This is due not only to the orbital wobble, but also to the small diameters of the stars and the fact that the orbital plane of the stars is not exactly edge-on to our line of sight. It just so happened that the astronomers caught the planet while it was transiting.
Because of the orbital wobble, the orbit continuously moves up or down relative to our view. This change is large enough that sometimes it misses passing in front of the stars, as seen from Earth.
The astronomers are still trying to explain why this planet is out of alignment with its stars.
“There could be other planetary bodies in the system that tilted the orbit. Or, it could be that a third star nearby that is a visual companion may actually be gravitationally bound to the system and exerting an influence,” they said.
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Veselin B. Kostov et al. 2014. Kepler-413b: a slightly misaligned, Neptune-size transiting circumbinary planet. ApJ, accepted for publication; arXiv: 1401.7275
